With the increasing social requirement on environmental protection, our country has put more and more efforts into environmental protection and appropriate polices regarding vehicle emission have been put forward by relevant national departments, and especially, introduction of ‘National Standard IV’ results in more stringent control for vehicle emission, which means that the standard can be met only after 30%-50% of pollutant is reduced on the basis of ‘National Standard IV’, and ‘National Standard IV’ will come into force nationwide on 2012 in accordance with normal standard implementation procedure.
Now, it is acknowledged that the technology of selective catalytic reduction (SCR) has dominated among vehicle emission post-treatment technologies, that is, a reducing agent is quantitatively injected into an exhaust pipe by atomization and the primary harmful gas NOX in exhaust gas is converted through an SCR catalyst into nitrogen and water which are then discharged out, thus the purpose of exhaust purification is achieved, and this is also the commonest technical route for reaching the ‘National Standard IV’.
An SCR system generally includes a liquid storage box, a metering injection unit, a nozzle and the like, however in the prior art, the modular units above are all independent of each other and the reducing agent in the liquid storage box and the metering injection unit is heated in an independent electric heating way or other heating ways, which consequently leads to complex connection between pipe and joint in the system, high possibility of leakage, complex structure under the independent electric heating way or other heating ways and low utilization rate of energy.